A plasticizer is a material incorporated in a plastic to increase the workability, flexibility or distensibility (elongation) of the plastic. Plasticization on the molecular level, according to theory, is the weakening or rupturing of selective "bonds" while leaving others strong to make possible the shaping, flexing or molding of the material being plasticized.
Although natural plasticizers, e.g., water, camphor, oils, pitch, etc., have been used since the earliest days of recorded history, it has only been since the early 1900's that synthetic materials have been used to plasticize resins and polymers. Since the advent of polyvinyl chloride (PVC), the most generally used synthetic plasticizers have been the esters of phthalic and phosphorus acids, e.g., dioctyl phthalate, diphenyl phthalate, tricresyl phthalate, triphenyl phosphate and the like. Monomeric plasticizers, while admirably fulfilling their function of external plasticization of PVC, have lately come under increasing pressure from environmentalists since they are known to "bloom", i.e., exude to the surface of a plasticized polymer and migrate to other materials in contact therewith. Despite the regulatory status and long safe history of plasticizer usage, the migration of phthalates and other plasticizers to medical and food products has caused considerable concern and incentive to search for truly permanent external plasticizer systems.
Because of the shortcomings of conventional monomeric plasticizers, e.g., volatility, extractability and migration, a considerable amount of research has been conducted in an effort to develop a truly permanent, high molecular weight polymeric modifier for PVC which is nonfugitive. The term "plastifier" has been coined to describe such modifiers to distinguish them from the conventional liquid to semi-solid type external plasticizers, usually monomeric, heretofore used as modifiers for PVC. The need is obvious for a plastifier which would have the properties of high permanence in the plastified system and good efficiency combined with a low order of toxicity and environmental safety.